Transit vehicle generated voltage control apparatus and method

ABSTRACT

There is disclosed a programmed microprocessor control apparatus and method for controlling the generated current of a transit vehicle electric motor in relation to a desired limit for the supply line voltage. The supply line volts are sensed and used for controlling the current generated by the transit vehicle motor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to the following concurrently filedpatent applications which are assigned to the same assignee as thepresent application; the respective disclosures of which areincorporated herein by reference:

Ser. No. 709,687, Case W.E. 46,848, which was filed on July 29, 1976 byJ. H. Franz and entitled Transit Vehicle Chopper Control Apparatus AndMethod;

Ser. No. 709,686, Case W.E. 46,849, which was filed on July 29, 1976 byL. W. Anderson, J. H. Franz and T. C. Matty and entitled Transit VehicleMotor Operation Control Apparatus And Method;

Ser. No. 709,821, Case W.E. 46,456, which was filed on July 29, 1976 byT. C. Matty and entitled Transit Vehicle Motor Effort Control ApparatusAnd Method; and

Ser. No. 709,684, Case W.E. 46,851, which was filed on July 29, 1976 byT. C. Matty and J. H. Franz and entitled Transit Vehicle ElectricalBrake Control Apparatus And Method.

BACKGROUND OF THE INVENTION

The present invention relates to the application of thyristor chopperapparatus for determining the propulsion power and electric brakeoperations of a transit vehicle having series propulsion motors, andmore particularly to control apparatus including a microprocessor thatis programmed for the desired control of such thyristor chopperapparatus.

Direct current power has been supplied to the series propulsion motorsof a transit vehicle with a thyristor chopper, such as disclosed in U.S.Pat. No. 3,530,503 of H. C. Appelo et al, for controlling theacceleration and speed of the vehicle by turning the propulsion motorcurrent ON and OFF in a predetermined pattern. The thyristor chopper canprovide either regenerative braking or dynamic braking when braking isdesired.

In an article entitled Automatic Train Control Concepts Are ImplementedBy Modern Equipment published in the Westinghouse Engineer for September1972 at pages 145 to 151, and in an article entitled Propulsion ControlFor Passenger Trains Provides High Speed Service published in theWestinghouse Engineer for September 1970 at pages 143 to 149, there isdescribed the operation of the P signal for controlling all poweredvehicles in a train to contribute the same amount of propulsion orbraking effort.

In an article entitled Alternative Systems For Rapid Transit PropulsionAnd Electrical Braking, published in the Westinghouse Engineer forMarch, 1973, at pages 34-41, there is described a thyristor choppercontrol system for propulsion and electrical braking of transitvehicles. The thyristor chopper provides a propulsion system that issuperior in smoothness and ease of maintaining a given speed, whichlatter feature provides the desired automatic train control. Moreover,the thyristor system makes regenerative braking practical because theresponse is fast enough to continuously match regenerated voltage toline voltage, and that matching prevents excursions in braking currentand torque due to sudden transients in line voltage. The reduction inpower consumption that results from regenerative braking can besignificant, but another advantage is in relation to minimizing heatinput to tunnels otherwise caused by dynamic braking.

The use of presently available microprocessor devices, such as the Intel8080 family of devices, is described in a published article entitledMicroprocessors -- Designers Gain New Freedom As Options Multiply inElectronics Magazine for Apr. 15, 1976 at page 78 and in a publishedarticle entitled Is There A High-Level Language In Your Microcomputer'sFuture? in EDN Magazine for May 20, 1976 at page 62.

SUMMARY OF THE INVENTION

A programmed microprocessor apparatus operates to control the generatedcurrent of a transit vehicle motor operative with a chopper in relationto a plurality of sensed supply line voltage levels. For a first toohigh level of supply line voltage, the generated current is reduced andfor a second higher level of supply line voltage the generated currentis further reduced and so forth in a progressive manner until at thehighest level of supply line voltage the chopper controlling thegenerated current is not turned ON.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a functional showing of the present control apparatus inrelation to the input signals and the output signals operative with thecontrol apparatus;

FIG. 2 illustrates the input signal operations and the output signaloperations of the present control apparatus;

FIGS. 3A and 3B illustrate schematically the provided interface of thepresent control apparatus;

FIG. 4 illustrates schematically a prior art braking mode of operationfor a motor;

FIG. 5 illustrates the coding of the program listing included in theappendix;

FIG. 6 shows a performance chart for a third actual operation of thepresent control apparatus with two vehicles working together in powerand in brake, for a partially receptive power supply line;

FIG. 7 shows a well known operational characteristic curve for a typicalseries propulsion motor operative with a train vehicle and the presentcontrol apparatus; and

FIG. 8 illustrates the here provided limit control of the supply linevoltage.

DESCRIPTION OF A PREFERRED EMBODIMENT

In FIG. 1 there is shown a functional illustration of the presentcontrol apparatus in relation to the input signals and the ouptutsignals operative therewith, and including a CPU microprocessor 94operative with a PROM programmable memory 96 and a scratch pad RAMrandom access memory 98 used for intermediate storage. The applicationprogram, in accordance with the program listing included in theAppendix, is stored in the programmable memory 96. The microprocessor 94can be an INTEL 8080, the random access memory 98 can be an INTEL 8101,and the programmable memory 96 can be an INTEL 1702 programmable readonly memory, which items are currently available in the openmarketplace. There are four illustrated categories of input and outputsignals relative to the controlled process operation of a transitvehicle. The digital input signals are supplied through digital input100 from the transit vehicle and include the slip slide signal SLIP, thethyristor temperature sensor thermal overload signal THOUL, theeffective value of the line filter capacitor as indicated by the fusecounter signal FUSE, the power circuit condition indication signal LCOC,the power and brake feedback signal BFEED, the field shunt feedbacksignal FS, the brake status signal BRKI and the clock signal 218 Hz. Theanalog input signals are supplied through analog input 102 and includethe first propulsion motor leg current I1, the second propulsion motorleg current I2, the line current IL, the line voltage LV, the primarypower request or brake request control signal P, the air pressure in thevehicle support bag members providing load weighed current requestsignal IRW, the analog phase signal IP and the vehicle actual speedsignal S1. The digital output signals are supplied through digitaloutput 104 to the controlled transit vehicle and include the line switchcontrol signal LS, the power brake mode control signal P/B, the fieldshunt control signal FS, the first braking resistor control signal BC1,the second braking resistor control signal BC2, the third brakingresistor control signal BC3, the zero ohm field shunt control signalBDC, the 10 kilometer per hour signal 10 KPH, the 25 kilometer per hoursignal 25 KPH, the phase zero control signal φ_(o), the timing signalBOOST, the ON suppress control signal SUPP and the zero speed signal ZS.The analog output current request signal I+ is supplied through analogoutput 106 going to an analog phase controller 108 operative to supplythe control signal ON to fire the chopper thyristor T1, the controlsignal OFF to fire the commutating chopper thyristor T3, the controlsignal T5 for the T5 thyristor in the propulsion motor control chopperapparatus and the analog phase indication signal IP going to analoginput 102. The time period associated with turning the chopper ON andOFF is at a constant frequency of 218 Hz, that defines the clock timeinterval for the program cycle and for checking the process operation.During each of the 218 time intervals per second, the program cycleoperates through the application program. It was necessary in the priorart for some of the input signals to be filtered to slow down theeffects of noise transients and the like, but the computer program nowsamples the input signals 218 times every second, so if desired eachsignal can be checked during each program cycle and if the signal staysthe same as it was before the proper response can be provided. Bysampling all the input signals, every program cycle, and by addressingevery output signal every program cycle, if noise transients arereceived, their effect can be minimized or eliminated. For the outputsignals, a correct output can be given 5 milliseconds later and fasterthan the power response time of the train vehicle. For the inputsignals, digital filtering by comparison with old data can eliminatetransient effects.

The train control system operative with each vehicle provides a P signalwhich selects a desired propulsion effort and this signal goes from 0 to100 milliamps and establishes how much propulsion power or brakingeffort is desired by a particular train vehicle. The P signal is decodedto determine the proper motor current to generate the proper effort. Inaddition, there is a confirming signal, called the BRKI signal whichdetermines when propulsion power and when braking effort is applied. Thepurpose of the BRKI signal is to control the power switching at thecorrect time to avoid one car braking while another car is inpropulsion. Contact closures in the power circuitry are detected toestablish that the power contacts have been made up properly and toreadjust the settings in the logic. For instance, in field shuntoperation, the amount of motor current is adjusted to keep from gettingan undesired physical jerk of the vehicle. A failsafe reading of the Psignal level is made such that, should the P signal be lost, the traincontrol automatically goes into a brake mode. The present propulsioncontrol apparatus determines which switches to close and when to closethem to modify the power circuit properly. A dynamic brake feedbacksignal is sent to the mechanical brake control for providing theblending of mechanical brake necessary to maintain the decelerationlevel required by the P signal. The P signal is in reality a vehicleacceleration or deceleration request.

The propulsion control apparatus provides output pulses to the mainpower thyristors to tell them when to turn ON and when to turn OFF. Whena command signal is sensed, for example, if the vehicle is in propulsionor power mode and the command signal desires the vehicle to brake, thecontrol apparatus senses any difference between the desired motorcurrent and the actual motor current and ramps down the actual currentas required. When the current gets down to a desired level, the controlapparatus opens all the propulsion switches and reconnects for a brakeoperation, then ramps the motor current back up again to the levelestablished by the desired brake operation.

In FIG. 2 there is illustrated the input signal operations and theoutput signal operations of the present control apparatus, including themicroprocessor 94 operative with its random access memory 98 and itsprogrammable memory 96. The analog input signals are supplied throughthe analog input 102, through the multiplexer 120 and analog-to-digitalconverter 122 and input port 124 of the microprocessor 94 operative witha data bus 126 and the address bus 128. The address bus 128 and data bus126 are operative through an output port 130 to control the multiplexer120 and the analog-to-digital converter 122. The digital input signalsare supplied through the digital input 100 operating through buffer 132with the input port 136 operative with the data bus 126 and the addressbus 128. The digital output signals are supplied through digital output104 including output ports 140 and 142 and respective isolation circuits144 and 146 with drivers 148 and 150 in relation to the data bus 126 andthe address bus 128. The analog output 106 is operative through outputports 152 and 154 through a buffer 156 and a digital-to-analog converter158 with the analog phase controller 108.

The central processor 94 addresses a particular input port or outputport or memory location and then transmits data to or receives data fromthat location on the data bus 126. For example, the central processor 94can address an input port, such as input port 124 for theanalog-to-digital converter 122 and the multiplexer 120. First, itpresents data to output 130 to tell the multiplexer 120 which analogcircuit input signal is desired. Each analog signal has some sort ofbuffering, such as a differential amplifier or a low pass filter. Whenthe particular input is addressed, the analog-to-digital converter 122cycles for converting that data. The digital feedback signals from thedigital feedback 100 come in and are read whenever desired. A monitor ordisplay panel 192 can be provided to indicate the state of operation ofthe central processor 94. The output port 153 is operative throughdigital-to-analog converter and buffer amplifier 194 with the providedtest point 190 and is operative with display 192. The manual switches196 are operative with input port 137 as shown.

The P signal goes through the multiplexer 120 to request a particularvehicle operation. The control processor 94 senses the various currents,the various voltages and the vehicle speed. It takes digital feedbacksignals through buffers to know what is going on in the power circuit inrelation to currents and voltages. The control processor 94 providesoutput command signals to the power circuit. Command signals go on the adata bus and output ports function as latches so the control processor94 can proceed to do other things while each latch remembers what is onthe data bus at a given address. The control processor 94 outputs asignal to close whatever power switches are desired and also outputs arequested motor current. The requested motor current is decoded in adigital-to-analog converter. The analog motor control circuit, inresponse to this current request, senses the actual motor current andthe commutating capacitor voltage, and if everything is satisfactory,the motor control circuit appropriately fires the drivers for thechopper apparatus.

In relation to effort versus motor current, at up to about 100 amps, atypical series propulsion motor as shown by FIG. 7 provides littlepractical effort, and above 100 amps the characteristic looks more orless like a straight line. As speed increases, there is wind resistance,so the effective effort available is actually less in power, and inbraking, the reverse is true. When power is requested, motor currentcomes up to the level requested by the P signal at a jerk limited rate.The vehicle increases its speed because of the effort supplied. Thephase increases with speed, and when the phase approaches almost 100%,the full field operation is completed and the field shunt is used toweaken the motor field, and this provides a transient response problem;a very fast controller is required, such that it can properly controlthe phase on the thyristors. In actual practice, propulsion power iseasier to control because in power a particular phase angle sets apercentage of line volts on the motor and this will give a particularamount of motor current, such that if the phase is set at 50%, aparticular amount of current is provided in power operation for a givenspeed. In brake operation, this same relationship is not true sincebrake operation is more unstable. If the phase is held at a desiredplace in power operation, the motor current is stable; if a particularphase setting is held in brake operation, the motor may go to overloador to zero. If it is desired to initiate brake operation, the controlapparatus has to command brake which ramps down the motor current on anjerk limit, then opens up the power switches and reconnects the powerswitches for brake operation; thereafter, the control apparatus goesinto brake operation and ramps up the motor current to give the torquenecessary to get the desired brake effort. The motor may be generating aconsiderable voltage that goes back into the supply line so a resistoris put into the circuit to dissipate the excess voltage. As the vehiclecomes down in speed, the motor counter EMF drops and the chopper can nolonger sustains the motor current, so switches are operated to changethe resistors to maintain the desired motor current. If the line voltageexceeds a particular value to indicate that the line is not receptiveand won't accept the generated current, the motor current is reduced ifno dynamic braking resistor is used. With dynamic resistors in thecircuit if the line voltage becomes excessive, the motor current isshunted into the dynamic braking resistor.

In FIGS. 3A and 3B there is schematically illustrated the providedinterface of the present chopper logic control apparatus. The digitalinput 100 is shown in FIG. 3B operative through the buffers 132 with theinput port 136. The analog input 102 is shown in FIG. 3A operativethrough multiplexer 102 and the analog to digital converter 122 with theinput port 124 of the microprocessor. The output port 130 is operativewith the register 131 to control the multiplexer 120 and the analog todigital converter 122. The output port 152 is shown in FIG. 3A operativewith the digital to analog converter 158 and the analog phase controller108; the output port 106 is shown in FIGS. 3A and 3B operative throughbuffer amplifiers 156 with the drivers 109, 111 and 113 for controllingthe respective thyristors T1, T2 and T5. The output port 142 is shown inFIG. 3B operative with the isolation amplifiers 146. The output port 140is shown in FIG. 3B operative with the isolation amplifiers 144. Theoutput port 153 is shown in FIG. 3B operative with isolation amplifiers194 and test point 190 and operative with display 192.

The pump circuit 151 operates to verify the proper working of thepresent control apparatus including the microprocessor 94 before theline switch is picked up and the desired propulsion motor controloperation takes place. A dummy boost signal is initially put out atprogram line 16 to enable the line switch to be picked up, and duringthe main program operation if something goes wrong the boost signaldisappears and the line switch drops out. The Y carrier shown in FIG. 5has added to it the boost bit, and then time is called to wait as shownby the code sheet; the Y carrier indicates whether the OFF suppress orthe ON suppress is called for.

The load weighed current request signal is output by amplifier 153. Thenthe buffer 155 leads to the phase controller amplifier 157, which takesthe current request signal from buffer 155 and the motor current signalsI1 and I2 from lines 159 and 161. The output of controller amplifier 157is the requested OFF pulse position or the phase angle IP. The output ofthe amplifier 157 is compared by comparator 163 with the timing rampfrom amplifier 165 which is reset by the computer each 218 hertz. Thecomparator 163 establishes when phase angle signal IP has exceeded thetiming ramp, and this would determine at the output of comparator 163where the OFF pulse is positioned. The logic block 167 determineswhether or not the OFF pulse position output of comparator 163 isactually used. For example, if comparator 169 determines there is toomuch current in the system, the OFF pulse will be fired and mightinhibit or suppress the ON pulse in logic block 171 which is operativewith the ON pulse. The boost pulse comes from the computer and goes intothe logic block 167 on line 173, and will fire an OFF pulse on theleading edge if comparator 169 has not already fired a pulse andsuppress any further action out of the control system. The logic block167 includes a flip-flop operative such that if an OFF pulse is firedonce during a given program cycle, a second OFF pulse is not firedduring that same program cycle. The power up restart circuit 175suppresses pulses until the control system has time to operate properly.The circuit 177 is a monostable to assure that only a pulse is output,and circuit amplifier 111 drives the OFF pulse going to the gated pulseamplifier for the thyristor T2. In power mode the FET switch 179 isclosed to provide the desired motor characteristics compensation signal,and in brake mode, this switch is opened to provide a faster controlleroperation. The amplifier 181 checks the phase controller 157 to see ifthe signal IP is all the way up against the bottom stop to indicate toomuch current, and if so, the circuit 171 suppresses the ON pulses; thisis used when starting up in power to skip ON pulses. The ON pulses aresuppressed by the power up circuit 183. The ON pulses use the monostable185 and the driver 109 as in the operation for the OFF pulses. thesafety enable signal or pump circuit 151 will stop the firing of an ONpulse if repetitive boost signals are not provided. The FET switch 187energizes the line switch output, such that if there is no activity onboost signal line 173, then the pump circuit 151 will cause FET switch187 to keep the line switch dropped. The T5 signal comes from thecomputer to fire the T5 thyristor, and monostable 189 drives the drivercircuit 191 going outside to the gated pulse amplifier for the T5thyristor. The phase controller 108 includes the operational amplifier157, with its attendant compensation for power and brake operations. Thecomputer can force the controller 108 from output port 3-0 to zero forstartup. The pumping circuit 151 checks the activity of the computer bylooking at the boost line 173 for snubbing the provision of ON pulsesand thereby controls the line switch. If the line switch is out, thepropulsion and brake control system cannot operate the chopperapparatus, so if something is wrong, it is important to snub the ONpulses quickly, because the line switch takes time to drop out; for thisreason an effort is made to stop the ON pulses when some controlapparatus malfunction occurs and is sensed by the boost signals nolonger being provided.

FIG. 4 illustrates the well known braking mode of operation of thecontrol apparatus, where the motors 700, 702, 704 and 706 arereconnected by means of a power brake changeover PBC. The circuit isarranged for regenerative or dynamic braking with the motors operatingas self-excited generators. The fields 902, 904, 906 and 908 arecross-connected to force load division between the paralleledgenerators. In regenerative braking the chopper ON and OFF ratio isregulated to maintain the desired current, with the more currentproviding the more braking. When the chopper 800 is turned ON, thecurrent in the motors increases. When the chopper 800 is turned OFF, thecurrent flowing in the chopper 800 is forced into the line 708 throughthe free-wheeling diode 814 by the motor reactor 812. The logic systemfor control of the chopper 800 during braking also monitors the voltageacross the line filter capacitor 910, and controls the chopper ON andOFF ratio in such a manner as to prevent the capacitor 910 voltage fromexceeding the line voltage 708, a condition that could result inincreasing current during the chopper OFF time and loss of brakingcontrol. If the capacitor 910 voltage during regeneration reaches apreset limit, the logic removes regenerative braking by turning thechopper 800 OFF and keeping it OFF, with the remainder of the brakingbeing achieved by friction brakes. The DC series motor acts as a seriesgenerator and inherently has a maximum generated voltage approximatelytwice the line voltage. To provide for the maximum energy regeneration,resistors R2, R3 and R4 are connected in series with the motors and theline by the power brake changeover PBC. The IR drop across the resistorsopposes the generator voltage so that the voltage across the capacitor910 does not exceed the voltage of line 708. As speed is reduced due tobraking, the voltage of the series generators drops. When the ON and OFFratio of the chopper 800 reaches the point where the OFF time is aminimum in order to maintain the motor current at the desired averagevalue, the logic system triggers pickup of one of the shortingcontactors BC1, BC2 or BC3, which reduces the IR drop in series with thegenerators in order that the chopper 800 can continue to maintainsubstantially the same average braking current. The chopper 800 shiftsfrom a minimum OFF condition to a minimum ON condition whenever ashorting contactor is picked up. In normal train operation regenerationof power into the power supply sometimes is not possible because of adead third rail, loss of third rail power in the car or the absence ofload being taken from the third rail. In that event the circuitconsisting of thyristor T5 and resistor R1 provides almost instantaneousshift from regeneration to dynamic braking. The logic that controls thebraking current makes the decision at the time of each ON pulse as towhether T5 only will be turned ON or the chopper 800 also will be fired.If the logic determines that the power supply is not receptive toregenerated energy, the chopper 800 is not turned ON and only T5 isgated to divert the motor current through the resistor R1. At the timeof the next fixed ON pulse the logic again determines the need to firethe chopper 800 on the basis of power supply 708 receptivity. Only whenthe line 708 again becomes receptive will the chopper 800 be gated andpermit the voltage generated to rise to the point where motor currentagain flows into the line 708.

FIG. 5 illustrates a code sheet that was used to develop the programlisting included in the Appendix. As shown in FIG. 5 and in reference toFIG. 2, output port 1 (shown in FIG. 2 as 153) was used for a test mode,output port 3 (shown in FIG. 2 as 154) was used for analog manipulation,output port 4 (shown in FIG. 2 as 152) was used for analog commandsignal output, output port 5 (shown in FIG. 2 as 142) and output port 6(shown in FIG. 2 divided into four bits each for 140 and 130) were usedfor digital command signal outputs, input port 4 (shown in FIG. 2 as136) was used for digital input data, input port 5 (shown in FIG. 2 as124) was used for analog input data and input port 6 (shown in FIG. 2 as137) was used for test purposes in relation to manual input switches.

FIG. 6 illustrates performance charts for the actual operation with apartially receptive supply line of the present control apparatus with atwo vehicle train. These charts show the effects of trying to have aregeneration operation without the line being fully receptive. The curve440 shows the line voltage. This is an effort during regeneration to putas much power back into the supply line as can be practicallyaccomplished, and this is done by raising the line voltage up to alimit. The charts shown in FIG. 6 illustrate the superior performance ofthe present control apparatus including the microprocessor compared toprior art type of control logic apparatus for the reason that thecomputer program enables a better comparison of the line voltage withthe generated voltage and a better control of cutting back the motorcurrent each time the computer program cycles, which current is cut backby changing the ON-OFF ratio cycle of the chopper apparatus supplyingthe motor current. The prior art control apparatus cannot function inthis way in that for each of the desired levels of action, dependingupon the level of voltage, a different control circuit would berequired.

In FIG. 7 there is shown a motor characteristic for a well-known seriesWestinghouse traction motor of Type 1463 operative through a 5.58 to 1gear ratio with 30 inch vehicle wheels.

As shown in FIG. 8 and program lines 147 to 151 in relation to excessivesupply line volts as the supply line voltage goes higher, the retardeffort parameter RE is correspondingly increased in a steppedrelationship having a digital non-linearity characteristic in an effortto provide a controlled effective asymptote limit on the supply linevoltage value in the order of 890 volts in a stepped function. Thisoperation provides a faster reduction of the retard effort parameter REthan will be recovered at the one unit every three program cycles, inaccordance with the program line 76. This increase in RE provided byprogram lines 147 to 151 can happen in one program cycle and it can takeevery three cycles times nine units or 27 program cycles to reduce REdown toward zero.

As shown in FIG. 6, the line voltage 440 is sensed and as it rises a BCresistor contactor shown in FIG. 4 is closed which changes the motorcircuit characteristics. When the motor current rises, the line voltagestarts to rise and the retard effort parameter RE functions to rapidlypull back the line current. When a BC contactor is closed, this picks upmore line current because a resistor is removed from the motor circuitand the line voltage starts to rise. If the line voltage goes too high,the RE parameter function lowers the motor current and this reduces theline voltage. The power supply line is receptive to only so much currentand if more current is supplied to the supply line, the supply linevoltage will rise as shown by the blips in the line voltage curve 440. Avery fast response is required, but a controlled operation is requiredto avoid a relaxation oscillator effect. The curve shown in FIG. 6relates to a partially receptive supply line that can accept only somuch amperes from a decelerating train vehicle. A braking resistor thatwas dissipating several kilowatts of power has disappeared and thesupply line cannot accept all of those kilowatts so the retard effortparameter RE function will operate to correspondingly lower the motorcurrent and keep the system in control.

If the generated voltage in brake mode rises above a predeterminedspecific limit, it is not desired to put back into the power supply linea voltage greater than this limit, because in effect the regeneratingvehicle is now the power supplier. The line voltage power supplyincludes a substation rectifier, and if the vehicle regenerated voltageis higher than what the rectifier is normally providing this can resultin a shut off of the diodes in the rectifier substation.

For this reason, in effect an absolute regenerated voltage limit isestablished as shown by FIG. 8. The regenerated voltage level and thelevel of current which is supplied by the train vehicle is determined bythe desired brake effort, because there is a given motor characteristicas shown in FIG. 7, and for any particular force or torque in the motor,a certain current level is needed and that current level also definesthe voltage level. The motor characteristic for a certain braking rateshows a line called braking effort, in accordance with a specified gearratio and the diameter of vehicle wheels, to establish a retarding forceto achieve a certain braking rate. If the mass of the vehicle is known,and the deceleration rate that is desired and the number of motors areknown, a calculation can be made of the brake effort force that isneeded to achieve the desired rate, and this in turn establishes thecurrent in that motor. The motor is operating as a generator giving somany amperes of current to provide a braking force of so many poundsthat is needed.

The typical limit for supply line voltage is in the order of 750 volts,which is a typical voltage as seen on the third rail, and the maximumlimit that is normally imposed on the regenerated voltage is 900 volts.There are usually two motors in series, so it is necessary to double theindividual motor voltage. If the power circuit includes a group of twomotors in series and two motor groups in parallel, about 750 volts isprovided by each motor, so about 1500 volts is provided by the twomotors. To lower this voltage and as shown in FIG. 4, the brakingresistors R2, R3 and R4 can be inserted in series with the generatingmotors to absorb some of the excess voltage. The power or energy thatthe motor is generating is converted into heat through an IR dropprovided between the generating motor and the chopper and the line,which absorbs the additional and excess voltage.

The above assumes that the supply line receives regenerated energy fromthe vehicle, however in some instances the supply line cannot receiveany energy from the vehicle. For example, if the vehicle is going alongthe track and goes, from one substation area into another substationarea, where there is a break in the third rail connection, all of asudden within a fraction of a second the supply line cannot receive anyof the energy that the vehicle has been supplying. A basically inductivesystem is wound up supplying energy, and the line no longer can receivethis energy. If the supply line will take no regenerated energy from thevehicle, the generated current starts charging the line capacitor andstarts rising. The generated voltage is compared with the permittedhighest limit that is allowed, for example, 900 volts can be theabsolute limit. To have a control region of 50 volts, the control pointis moved down 50 volts, to give a permitted limit of 850 volts. If thegenerated voltage goes above this 850 volt limit, the present controlapparatus takes a voltage sample for each program cycle and provides animmediate response if a bigger voltage than the desired limit issampled. If a voltage above the limit is sensed, depending on how farabove it is, the program lines 147 to 151 provide a progressive cutback,depending on the magnitude of the voltage sample and how big the voltagesample is above the control limit of 850. The control apparatus willaccumulate the action that is taken in accordance with the differenceamount that the sample voltage is above the limit voltage. In theconfirmed brake mode of operation CYCBB, each cycle of the program thesupply line voltage is sensed and compared to this provided limit of,for example, 850 volts. If the line voltage is greater than a firstlimit of 850 volts at program line 147 then the retard effort RE isincreased to the RE plus two. If the line voltage is greater than asecond limit, for example 860 volts at program line 148, then the retardeffort RE is set to be RE plus two plus three. If the line voltage isgreater than a third limit, for example 870 volts, then the retardeffort is made RE plus two plus three plus four. If the sensed linevoltage is greater than a fourth limit, for example 880 volts at programline 150, then the retard effort RE is set to be RE plus two plus threeplus four plus five. If the sensed line voltage is greater than a fifthlimit, for example 890 volts at program line 151, then a totalsuppression of ON pulses is provided. The program performs thisoperation in time sequence. The value of RE determines the reduction ofthe motor current. When the sensed supply line voltage is below thefirst limit of 850 volts, the motor current is at a satisfactory leveland follows the current request without modifying the retard effortparameter RE for subtraction from that current request at program line113. The desired brake signal expressing a certain amount of brakingeffort is developed into a current request, and the retard effort RE issubtracted away from it during the next program cycle. The so modifiedcurrent request determines the phase angle of the chopper which iscontrolling motor current every program cycle. The external high-speedanalog phase controller shown in FIG. 1, as soon as this current requestis received by it, takes immediate action to move the chopper phaseangle in accordance with the desired motor current. By controlling thetime the chopper is ON, the control apparatus changes the motor current.The motor is operating as a generator and there is much inductance inthis circuit including the motor reactor. When the chopper is ON itprovides effectively a short across the generator circuit to put thegenerated voltage across the inductance and the resistance of thecircuit to determine the rate of change of current. When this choppershuts OFF, then the supply line voltage responds to the generatedvoltage from the motor. The average voltage across the chopper isestablished by the ratio or percentage of time the chopper is ON inrelation to the time the chopper is OFF. The retard effort RE is one ofthe factors that is used to make this ratio, and in addition the ratiois a function of speed, the current request, and the like.

To control the chopper apparatus, the present control operation issampling the generated voltage to determine the ON-OFF ratio of thechopper; an averaging is going on in relation to a current request, a Psignal, a motor current level, the vehicle speed and so forth to get anaverage; then when the line voltage rises above a predetermined limit asdetermined by sampling every program cycle, a predetermined pattern ofcutbacks on the current request is provided at program lines 147 to 151in a cyclic and accumulative action, with the last step being when theline voltage is greater than a last predetermined limit and the controlapparatus suppresses the ON pulses to inhibit turning the chopper ON foreach program cycle that the latter condition prevails and with thechopper OFF the motor current keeps dropping.

The prior art control approach was to fire the T5 thyristor, if the linevoltage rose above a predetermined level, by comparing the line voltagewith an absolute reference such as 850 volts; it was an analog controlwith filtering and as the line voltage started increasing the controlstarted turning ON the T5 thyristor shown in FIG. 4. One controlcomparison was made to control the chopper and a second control operatedwith a higher limit than 850 volts to control turning ON the T5thyristor. The present control operation stays with and eventually willturn OFF the chopper if desired, and this is important relative toenergy conservation, because as soon as the T5 thyristor is turned ONthis loses into the resistance all the energy that is available from themotor circuits. Normally the power supply line is capable of taking someamount of energy, since even a single car has an air conditioner, an aircompressor and can absorb a certain amount of energy even by itself.

The program listing included in the Appendix is written in a languagecalled PLM which was developed for use with the INTEL microprocessor,such as the central processor 94. This is a high level assembly languagewhich can be compiled into machine language. The numbers used in thelisting are in the hexadecimal number system, which is a base 16 numbersystem. The first part of the listing in lines 1 to 6 is for bookkeepingpurposes and identifies for the program the variables, the constants andthe labels used in the course of the program. More specifically, K is anartificial constant that is set in the brake mode for controlling thebrake build-up. IRW is the current request that has been load weighed tocompensate for the weight of the car. I0 is the old current, I1 is oneof the motor circuit currents and I2 is the other motor circuit current.IR is the current request. LVL is the line voltage. PR is the permissionto regenerate. RE is the retard the effort due to a number of conditionssuch as overline voltage or overcurrent or the like. TI is a timer. ILis line current. LV is line voltage. M is the mode of the externalequipment. M0 is the old mode and M1 is the transitory mode asdetermined by the mode request and the position of the power brakeswitch. N is a counter. PH is the phase that the external analogcontroller is controlling and that is brought back in to establish thefield shunting. PI is the P signal that is used internally to do modechanges, PN is the new presently read P signal and P0 is the jerklimited P signal. TT is a timer. SI is the speed after the hysteresishas been applied. TOS is blank. ZI and Q are carriers to the externalanalog controller and establishes certain modes of operation. S is thecurrently read speed signal and SS is the speed signal after it has beenmodified for the taper on the power and brake modes. T is a timer, TP isa timer and TS is a timer. X, X1, X2, Y and Z are external controls forthe analog controller. The three upper lines in the program listing arethe variables used in the program. The next three lines are labels thatidentify in the program certain starting points where the program canjump to if needed. The compiler assigns memory locations for eachvariable, and any time a given variable is read, the computer knows thememory location. The mode labels are used to assign locations in theprogram.

The program defines the desired sequence of steps to be followed incontrolling the propulsion and electric braking operation of a transitvehicle. The safe mode of operation is the brake mode. Therefore, thepresent control program listing always starts up through the brake mode.If an abnormal condition is detected, the program operation returns tothe beginning and resequences through the brake mode. In comparison, theprior art control sytems shut the chopper OFF and didn't try toreinitialize the equipment or to make sure the start of the operationwas always from the same base.

In line 8 and mode 1 of the program an output port is directed to take acertain state, which is output port 1, and the constant Q is initializedto equal zero. In lines 9 to 14 of mode 1 the program sets the outputline switch out and checks if it is satisfactory and then reads the linevoltage. The program looks at the inputs, the slip slides, and so forthto see that they are in proper form and then tests for line voltage. Ifthe line voltage at line 14 is not satisfactory, the program goes backto line 8 and the start. If the line voltage is satisfactory, a falseboost signal is output at line 16 of the program because the line switchcannot be picked up until a boost is provided, so a false boost isprovided for this purpose. The motors will not be energized at this timebecause the ON and OFF pulses for the thyristors have been suppressed.If the line voltage is all right, then in line 17 of mode 2 of theprogram the line switch is closed for charging the commutatingcapacitors and a check is made at line 18 to see if all the inputs areas desired, and if they are satisfactory, the program at lines 20 and 21initializes certain timer variables.

In line 24 of mode 3 of the program the program waits for a pulse froman external clock at 218 Hz from a crystal oscillator and when theprogram sees the rising edge of the clock pulse, it provides the frontend of the boost to fire the ON pulse and puts the ON pulse positionerup to output the request through output port 106 shown in FIG. 3.

Lines 26 to 30 of mode 4 of the program are controlling the externalanalog phase controller 108 to provide a boost interval for interpretingthe current signals and other things as to where the ON pulse will beand whether or not it is allowed, and providing the ON suppress and theOFF suppress.

In mode 5 lines 40 to 64, the program reads analog inputs and sets somevariables. The P signal which is a linear monotonic type signal isconverted to effort. When the P signal is above 60 milliamps, this is apower request, when the P signal is below 60 milliamps it is a brakerequest, and below 20 milliamps it is superbrake. If the line voltageLVL is less than some predetermined number then the operator RE is setto retard the effort. In addition, a speed taper is provided whereby thespeed signal S is read in the outside world and is modified so that theinternal speed signal SS stays at the given level as long as theexternal speed signal is within predetermined limits. The external speedS is the actual vehicle speed and the internal speed SS is the valuethat the program is using for its operations. In effect a window is puton the real vehicle speed and then used inside the program as abracketed speed such that as the outside speed starts moving up, thenthe inside speed SS doesn't change for as long as the outside speed A iswithin this provided window, thereby if the outside speed S has noiseinterference, this provides a dead band for filtering the noise andother disturbances out of the actual speed signal S.

In lines 32 to 38 of mode 6, a determination is made to go to power orgo to brake and to confirm that the control is in power or the controlis in brake for the purpose of setting up the request.

Starting at line 65 of mode 7, the P signal is considered, which Psignal has a value from 0 to 100, for the generation of requestedeffort. If the control is in power and the P signal is above 60milliamps, this requires more effort. If the P signal is below 60milliamps and the control is in power, this maintains a minimum effort.If the control is set in brake and the P signal is below 60 milliamps,this requests an increased brake effort down to 20 milliamps, at whichtime the same effort is held. If the P signal is above 60 milliamps butthe BRK signal does not allow the control to go into power, a minimumbrake effort is maintained. In addition, a jerk limit is provided inlines 75 to 82 of the program because the P signal can change instantlyto a full 100 milliamps and must be jerk limited such that the effortsignal has to increase on a ramp in one program cycle step at a time.The jerk limited P signal is incremented by one unit each program cycleto provide the desired ramp and repeatedly incrementing one at a timedetermines how quick the effort increases. When going into brake toprevent an abrupt fade-out of the electric motors and to permit asmoother blending of the friction brakes, a false fade-out is providedin lines 84 to 89 of the program so the electric braking fades out on asofter slope to permit the friction brakes to maintain a smooth andtotal braking effort.

Lines 94 to 98 of mode 8 of the program provides a check for a zerospeed when the actual speed is less than a defined amount such that thevehicle is considered to be standing still at zero speed. In addition,zero speed clears the Z carrier within the program used in a situationwhen there is too much current in brake, which indicates an overload andthe operation should be shut down. In line 99 of the program, if thevehicle is at zero speed and a request for power is received, then the Zcarrier is cleared to go back into power. A check is made at line 100 tosee if the line voltage is too low, and if it is too low, the programreturns to the beginning of the program since there is not enough energyfor the commutating capacitor and the present control apparatus is notrequired to operate below a predetermined voltage level, which couldmean that the vehicle is operating in a rail gap and the normal mode isto shut down the equipment when going into a rail gap. In addition inline 101 of mode 8, a check is made for excessive line voltage which isuse for incrementing the RE request. If the voltage is too high, the Ycarrier is set for the purpose of skipping ON pulses, and the RE requeststarts reducing the motor current and this reduces the line current. Acheck is made for LCOC which is a signal that indicates that all thepower circuitry is made up properly. If any of the conditions, such as athermal overload or a slip/slide signal or the like, indicates improperaction, the effort request is reduced and a suppression of the ON pulseis effected. The Y carrier controls the ON pulse, the OFF pulse and theT5 pulse. A check is made to see if motor current I1 is greater thanmotor current I2 or vice versa to maintain the desired balance in themotors. A check is made at line 105 to see that I0, which is a sum of I1and I2, is not exceeding the request IR by more than a certain amount;and if it is, the ON pulses are skipped.

The line current limit check in line 103 of mode 8 is provided toestablish that the respective currents in each of the motor circuits arewithin a predetermined match of each other in relation to balance; ifthey are, the operation is satisfactory; and if not, corrective actionis taken. Towing protection is provided in line 104 to enable a trainvehicle to be pulled or towed; if there is a failure in the externalequipment of a given vehicle, it is desired that this be recognized andthe vehicle operated such that the other operating cars in the train cantow the disabled vehicle.

In lines 110 to 113 of mode 9 of the program the current request isgenerated from the PR signal from which the retard effort RE issubtracted to get the IR request signal, and a speed tilt is provided inrelation to a power mode or brake mode of operation to change thecurrent request IR on the field shunt and check of the inputs. Theeffort request is the modified P signal which has been modified, then aspeed tilt is added to the modified P signal by looking at the speed andtilting the P signal plus when power operation is desired and tiltingthe P signal negative for brake operation. The speed tilt is provided inlines 114 and 115 by chopping off a little bit of the requested currentto compensate for the effort required to maintain acceleration as speedincreases; in effect, the requested current is added to or subtractedfrom, depending upon whether the control is in power or in brake, andthis adds or subtracts an increment of vehicle speed. In this regard,during brake, the motor is dragging and the car is dragging, so lesseffort is needed from the motor current because the drag is additive;however, in power operation, the drag is against the propulsion effort,so additional motor current and effort is provided to compensate for theneeded extra power to properly operate the vehicle. The provided speedtilt accomplishes this function in relation to the speed of the vehicle.For the change of the current request on field shunt in lines 116 to118, if in field shunt operation, then the motor characteristics aredifferent; the field shunt is field weakening, and there is a differentcurrent level needed to get the desired motor torque. The input check isprovided at lines 120 to 123 to make sure that all the switches and soforth are set where they should be. The input 4 relates to thetemperature of the semiconductors; this temperature in the prior art wassensed and if too high was previously used to shut everything down as anirrevocable control move. In the present system, restarting of theprogram is permitted after a too high semiconductor temperature issensed. Input 4 is presently checked to see if the temperature is nottoo high, if it is satisfactory the ON pulse for the chopper is allowed,and the incremental loop timer goes to mode 10. If the semiconductortemperature is too high, the program goes to mode 10 and if necessary, aT5 pulse is fired; for a given cycle of program operation, it may bedesired to cancel the ON pulse for that cycle or suppress the OFF pulseor shut off the T5 pulse, or even to turn on the T5, depending on whatis desired. If the semiconductor temperature in the next cycle is backto a desired level, the program continues as normal to avoid a totalshut-down and permit the transit vehicle to continue running. Thepresent control provides a lessening of the provided effort to permitthe equipment to continue running within capabilities and contributingsome partial desired effort to the train movement.

Mode 10 of the program includes four selectable controloperations--namely, CYCPP which is confirmed power, CYCBB which isconfirmed brake, CYCBP which is cycling from brake to power, and CYCPBwhich is cycling from power to brake. These relate to differences in thedesired vehicle control as to when a particular control is desired andwhat kind of control is desired. More specifically, for the firstcontrol operation of CYCPP which is confirmed power, it is desired tostay in power and to confirm that the control is presently in power; thefield shunt is closed in lines 129 to 132 in relation to phase angle andthe line voltage is cut back in line 134 in relation to low voltage. Theclose of the field shunt is provided to increase the train speed. Tokeep the current flowing in the motor, it is necessary to keep turningthe chopper ON for longer periods of time to keep increasing thepercentage of voltage to counteract the counter EMF of the motor. Atsome control point, it is desired to move to field weakening, and thecontrol approach taken here senses the chopper being ON for 95% of thetime and field weakening is then provided.

In the second operation of CYCBB which is confirmed brake, the requestis to be in brake and the control operation is confirmed to be alreadyin brake. This portion of the program permits improved control in thebraking mode in relation to regeneration of power, wherein a sequence ofcontrol steps is provided in lines 147 to 151 taking progressivelystronger action if the line voltage gets beyond defined limits in aneffort to control the maximum level of line voltage. If the line voltagestarts getting above a predetermined first limit CE, then the request iscut back by two; if the line voltage gets above a predetermined secondlimit D4, then the previous action has added to it a stronger reductionand so forth through greater predetermined limits to effectprogressively increased current reductions due to excess line volts bysuppressing ON pulses for the chopper to provide this current reduction.

A hysteresis for brake build-up is provided at lines 152 to 156 bytrying to get at least a minimum predetermined current level in thebrake mode after the motor armature has been reversed for braking; thisportion of the program provides the requested brake effort inconjunction with a minimum effort to assure an adequate brake current.The problem is to assure after the propulsion motors are established inthe proper way to start generating brake current, that the armaturecurrent is built up in time to prevent loss of the armature currentbecause when changing from power to electric braking, the brakingarmature current results from the residual magnetism left over in thefield circuits of the motor. If the control apparatus does not operatefast enough and lets this residual magnetism go to zero, the armaturecurrent will not build up. In relation to a contribution to regenerativebraking or electrical braking, the present control apparatus enables abuild up of brake current after going to the brake mode, such that whenthe build up contractor is closed thereafter only ON pulses are providedwith a defeat of OFF pulses until a minimum armature current is presentin an effort to assure that the armature current gets started as quicklyas it can and before there occurs a loss of the residual fieldmagnetism. The propulsion motor is a series motor, so the armature andfield windings are in series. After cutting the armature current to gointo a brake operation, it takes a while for the field to be reenergizedand this is the residual magnetism that is involved in this operation;the armature circuit is reversed for brake operation, but the field doesnot go to zero instantly because of residual magnetism. When it isdesired to go into the brake mode of operation, the program maintains aminimum level of current in the brake mode and permits the armaturecurrent build up in the opposite direction to an adequate level tomaintain the field magnetism and still reverse the current flow in thearmature; the control operation desires a current above a certain valueand assures that at least this value of armature current is maintained.##SPC1##

We claim:
 1. In control apparatus for a chopper operative with a powersupply line to energize an electric motor, the combination of:meansincluding said chopper for controlling the generated energy of the motorduring braking, means responsive to the voltage of the supply line;means for providing at least one predetermined limit for said supplyline voltage; and means for comparing said supply line voltage with saidlimit and coupled with said generated energy controlling means toprovide a predetermined reduction of the generated energy of said motorto establish the supply line voltage below said limit.
 2. The controlapparatus of claim 1, with a plurality of successive predeterminedlimits being provided for said voltage, and with said comparing meansdetermining a specified reduction in said generated energy in relationto each of said limits.
 3. The control apparatus of claim 1, with thechopper having an ON operation, and with said comparing meanscontrolling the ON operation of the chopper to determine a specifiedreduction in the generated energy of the motor in relation to said onelimit.
 4. The control apparatus of claim 1, with a plurality ofsuccessive limits being provided for the voltage, and with saidcomparing means determining a progressively larger reduction in thegenerated energy in relation to each of the successive limits for saidvoltage.
 5. In the method of controlling during braking the generatedenergy provided by an electric motor connected for operation with achopper to supply said energy to a power supply line, the stepsof:sensing the voltage of the power supply line; establishing aplurality of successively higher limits for said voltage; comparing thesupply line voltage with at least one of said limits; and controllingthe chopper to provide a predetermined reduction in said generatedenergy of said motor for each of said successively higher limits whensaid voltage is greater than one of said limits.
 6. The method of claim5, with the chopper having an ON operation and controlling the ONoperation of the chopper to reduce the generated energy when saidvoltage is greater than said limit.
 7. The method of claim 5, includingcontrolling the chopper to reduce the generated energy by respectivelylarger amounts in relation to said voltage being greater than thesuccessively higher limits for said voltage.
 8. The method of claim 5,with the chopper having an ON operation and an OFF operation, includingand reducing the ON operation of the chopper by progressively largeramounts in relation to said voltage being greater than said successivelyhigher limits until the chopper is in said OFF operation when saidvoltage is greater than the highest limit for said voltage.
 9. Incontrol apparatus for controlling the energy provided by an electricmotor to a power supply operative with that motor during braking, thecombination of:means for controlling the regenerated energy of the motorfor at least one of successive time intervals, means for sensing theactual power supply voltage during said one time interval, means forproviding at least one voltage reference, and means coupled with saidregenerated energy controlling means and limiting said power supplyvoltage by comparing the actual power supply voltage with said voltagereference during said one time interval for controlling said generatedenergy to provide a limit on the power supply voltage in relation tosaid regenerated energy.